Electrochemical oxidation and reduction

ABSTRACT

A process for electrolyzing material capable of being oxidized or reduced comprising forming a liquid permeable mixture of conductor particles, said conductor particles being of small particle size, electrically conductive, and insoluble in and unreactive to the electrolyte solution used in combination therewith, and material to be electrolyzed, said material being insoluble in and unreactive to the electrolyte solution used in combination therewith, in the physical form of particles of small particle size, and capable of being oxidized or reduced to yield products which are soluble in the electrolyte solution, in contact with an electrode and electrolyte solution, said electrolyte solution being capable of conducting electricity and of dissolving the products produced on oxidizing or reducing said material being electrolyzed but being incapable of dissolving said material to be electrolyzed or said conductor particles; immersing a counter-electrode in said electrolyte solution out of contact with said liquid permeable mixture of particles; and flowing electricity in a single direction between said electrode and said counter-electrode to oxidize or reduce said electrolyzable material thereby forming a solution in said electrolyte of the resultant oxidized or reduced material.

United States Patent 1 Voorhies John Davidson Voorhies, New Canaan, Conn.

[75] Inventor:

[73] Assignee: American Cyanamid Company,

Stamford, Conn.

[22] Filed: Feb. 14, 1972 [21] Appl. No.: 226,306

[52] US. Cl. 204/72; 204/73; 204/74;

[51] Int. Cl. .i (125B 3/00; C07C 85/00;

CO7C 39/08;C07C 107/00 [58} Field of Search 204/72 [56] References Cited UNITED STATES PATENTS 729,502 5/1903 Moest i. 204/78 1,322,580 11/1919 Kitchen... 204/78 X 3,392,093 7/1968 Smeltz 204/72 3,427,234 2/1969 Guthke et al. 204/73 A 3,573,178 3/1971 Blackman 204/59 L 3,640,803 2/1972 Frind 204/73 R Primary Examiner-F. C. Edmundson Attorney, Agent, or Firm Philip Mintz Dec. 9, 1975 57 ABSTRACT A process for electrolyzing material capable of being oxidized or reduced comprising forming a liquid permeable mixture of conductor particles, said conductor particles being of small particle size, electrically conductive, and insoluble in and unreactive to the electrolyte solution used in combination therewith, and material to be clectrolyzed, said material being insoluble in and unreactive to the electrolyte solution used in combination therewith, in the physical form of particles of small particle size, and capable of being oxidized or reduced to yield products which are soluble in the electrolyte solution, in contact with an electrode and electrolyte solution, said electrolyte solution being capable of conducting electricity and of dissolving the products produced on oxidizing or reducing said material being electrolyzed but being incapable of dissolving said material to be electrolyzed or said conductor particles; immersing a counter-electrode in said electrolyte solution out of contact with said liquid permeable mixture of particles; and flowing electricity in a single direction between said electrode and said counter-electrode to oxidize or reduce said electrolyzable material thereby forming a solution in said electrolyte of the resultant oxidized or reduced material,

5 Claims, N0 Drawings ELECTROCHEMICAL OXIDATION AND REDUCTION This invention relates to an improvement in the technology of electrolytic oxidation or reduction which greatly expands the utility of such technology.

Because of the readily apparent advantages of performing oxidation or reduction electrolytically rather than chemically, many attempts have been made to develop commercial applications utilizing such technol' ogy. With few notable exceptions, these attempts have been unsuccessful. Among the handicaps responsible for such limited application are (l) low cell capacity due to the slow rate at which such processes operated resulting in the need for large equipment for a given throughput and (2) the limitations due to the low solubility or insolubility of many organic substances in aqueous electrolytes. The present invention overcomes these handicaps.

Conventional electrolysis systems utilize an anode, a cathode, and an electrolyte with the material to be electrolyzed being dissolved in the electrolyte. Such systems suffer from the handicaps listed above. Sometimes, when the material to be electrolyzed is insoluble in the electrolyte, it is possible to find a mutual solvent for the material to be electrolyzed and the electrolyte or to emulsify the material to be electrolyzed in the electrolyte in order to permit use of this process. Finding such mutual solvents or suitable emulsifiers is difficult and complicates the process since (a) additional materials must be introduced and recovered, (b) such mutual solvent or such emulsifier may also be oxidized or reduced producing unwanted byproducts and lessening the electrical efficiency of the cell. Another problem sometimes encountered is the inhibiting effect of the electrolysis products on the working electrode.

in accordance with the present invention, these problems are overcome and other advantages as will be apparent hereinafter are obtained by using, as one electrode of the electrolytic cell a liquid permeable mixture of conductor particles and particles of the insoluble material to be electrolyzed. When direct current flows between this composite electrode and a counter-electrode through an electrolyte solution, the material to be electrolyzed is oxidized or reduced to form a product which is soluble in the electrolyte.

The conductor particles must be of small particle size, e.g. up to about 50 microns in diameter and preferably up to ID microns in diameter, and must be electrically conductive. It is also important that they be insoluble in and unreactive to the electrolyte solution used in combination therewith in the electrolysis cell. Illustrative of such conductor particles are metal powders, such as copper powder, lead powder, etc., although finely divided carbons, such as decolorizing charcoal, activated carbon, graphite powder, carbon black, etc., are preferred.

The material to be electrolyzed must also be insoluble in and unreactive to the electrolyte solution used in combination therewith in the electrolysis cell. It, too, should be in the physical form of small particles, such as a powder. Although the size of these particles is not critical, they should be small since the smaller they are, the faster the process becomes. This material must be capable of being oxidized or reduced to form a product which is soluble in the electrolyte solution, either directly or by reaction with the electrolyte solution. Ex-

amples of such materials include quinones, including vat dyes, which can be reduced to hydroquinones, such as the leuco form of the vat dyes, in basic electrolytes, nitro compounds which can be reduced through hydroxylamines to amines in acid electrolytes; azo compounds which can be reduced to hydrazo compounds in acid electrolytes; and amines which can be oxidized to quarternary ammonium compounds in basic electrolytes with which they react.

Illustrative of the quinoid compounds which are preferred for use as materials to be reduced in accordance with this invention are the l,2- and 1,4-quinones such as l,2-benzoquinone; 1,4-benzoquinone; l,2-naphthoquinone; l ,4-naphth oquinone; 9, l 0-anthraquinone; 1,4-anthraquinone; 9, l O-phenanthrenequinone; l ,2- benz-9, l O-anthraquinone; l ,2,5 ,6-dibenz-9, l0- anthraquinone; and derivatives thereof having inert substituents, such as alkyl, alkoxy, halogen, carboxyl, hydroxyl, amino, amido, etc., which are unaffected by and have no adverse influence on the reduction. Espe cially preferred for use in this process are vat dyes that contain a pair of carbon yl groups as a l,4-quinone or as part of a complex quinone system in a polycyclic aromatic compound. Such vat dyes include anthraquinone derivatives and anthrone derivatives. The antraquinone derivatives include l simple derivatives of anthraquinone such as acylamido anthraquinones, cyanuric acid derivatives, anthramides, and miscellaneous derivatives such as dianthraquinonyl ethylene, and (2) compounds in which heterocyclic ring is fused to the anthraquinone nucleus in the l,2- or 2,3 positions, such as carbazoles, imidazoles, oxazoles, thiazoles, acridones, thioxanthones, indanthrones, etc. The anthrone derivatives include (l) carbocyclic compounds, such as pyrene derivatives, benzanthrone derivatives, pyranthrones, napthodianthrones and anthradianthrones, dibenzopyrene quinones, anthranthrones, and miscellaneous homocyclic quinones and 2) 1,9-heterocyclic derivatives, such as flavanthrones, etc.

The electrolyte solution must be capable of conducting electricity, must not react with or dissolve the material to be electrolyzed, but must be capable of dissolving the oxidation or reduction product produced, either directly or by reaction therewith. Usually, such electrolyte solutions are aqueous solutions of acids, bases, or salts, such as hydrochloric acid, sulfuric acid, boric acid, phosphoric acid, hydrobromic acid, acetic acid, formic acid, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, tetramethylammonium hydroxide, sodium chloride, aluminum chloride, sodium sulfate, potassium nitrate, sodium acetate, etc. The electrolyte solution may also contain organic solvent, such as acetone, methanol, ethanol, methylethyl ketone, ethyl acetate, etc. to enhance the solubility of the oxidation or reduction products therein. It is also possible to use an organic solution of an ionizable salt, such as an amine hydrochloride, as the electrolyte solution, although such is not usually desirable because of the possibility of introducing competing electrolysis reactions.

A preferred procedure for preparing the liquid permeable mixture of particles to serve as the composite electrode is to form a slurry of the conductor particles and the material to be electrolyzed in a suitable liquid in which they are insoluble, preferably the electrolyte solution to be used in the electrolysis cell although other inert liquids can be used, and then filtering the slurry. The filter may be electrically conductive or may be provided with means, such as a metal screen, to conduct electricity to the base of the resultant filter cake. Continuous addition of electrolyte solution to maintain a body thereof in contact with the filter cake into which solution the counterelectrode is immersed out of 5 contact with the filter cake while continuously withdrawing through the filter cake electrolyte solution containing dissolved therein the electrolysis products while the direct current is flowing through the electrolysis cell provides an effective method for utilizing this invention. However, other modes of operation are also feasible. For example, the mixture of particles can be prepared by mulling together the conductor particles, the material to be electrolyzed, and electrolyte solution and the resultant mixture can be placed in a cup or tank having means to conduct electricity to the inside thereof, which cup or tank is immersed in a larger container containing electrolyte solution and one or more counterelectrodes.

EXAMPLE 1 An electrolytic cell comprising a container containing an electrolyte solution, an anode, and a cathodic counterelectrode was constructed. The electrolyte was an aqueous solution containing 17% zinc chloride and 27% ammonium chloride. The anode was a mixture in a suitable container of 1 1.42 grams of azobisbutylformamide particles with 200 milliliters of a carbon paste made by mulling high surface carbon powder with a small quantity of an aqueous solution containing 17% zinc chloride and 27% ammonium chloride. The counter-electrode was a carbon rod in a porous Alundum cup. The anode and the counter-electrode were both disposed in contact with the electrolyte solution but out of contact with each other.

An electric current at a potential of 3.0 volts was passed through the electrolytic cell for several hours to oxidize the azobisbutylformamide.

EXAMPLE 2 An anode was prepared by compressing a mixture of equal parts of carbon powder and 4,4-

EXAMPLE 3 An anode was prepared by packing a mixture of 8.47 grams of tetrakis( p-diethylam inophenyl )-pphenylenediamine(see U.S. Pat. No. 3,484,467, Example 3) and twice its volume of carbon black into a sin tered glass funnel and then saturating the mixture with about 200 milliliters of an electrolyte solution of 12.5 grams of sodium hexafluoroantimonate dissolved in a mixture of 400 milliliters of acetone and 100 milliliters of water. Three carbon rods served as anode contacts. The cathodic counter-electrode was a silver wire coil in a glass frit compartment pressed against the carbonamine mixture (The glass frit kept the counter-e1ec trode wire out of contact with the anode particles). Additional electrolyte solution was occasionally added to the cathodic compartment. A reference electrode was inserted into the carbon-amine mixture. An electric current was passed through the cell at 25-30 volts for several hours. Thereafter, bis(p-diethylaminophenyl) [N,N-bis(p-diethy laminophenyl )-p-aminopheny1 laminium hexafluoroantimonate was isolated from the electrolyte filtrate.

EXAMPLE 4 A coarsely fritted glass filter funnel of about one inch diameter, containing a glass fiber mat and a flat Nichrome wire spiral cathode contact, was packed with a mixture of 1.0 gram of anthraquinone and 1.0 gram of powdered carbon moistened with a 2% aqueous sodium hydroxide solution. Above the fritted filter and the anthraquinone-carbon mixture was suspended a small glass tube with a fritted end, the tube containing a graphite rod anodic counter-electrode. A reference electrode (Ag, AgCl, N/lO aqueous HCl) was inserted into the anthraquinonecarbon mixture. Sufficient electrolyte, 2% aqueous sodium hydroxide solution, was continuously added above the filter cake to maintain contact with the counter-electrode. The Nichrome wire spiral and the counter-electrode were connected to a source of direct current and the electrolytic cell was operated at 1.1 volts with a current of about 60 milliamperes until the current flow declined to a low value. The red filtrate resulting contained the reduction product anthrahydroquinone.

EXAMPLE 5 A mixture of 1.0 gram of anthraquinone and 2.0 grams of graphite powder moistened with 1N aqueous sodium hydroxide solution was packed into a stainless steel filter crucible of 35 micron porosity and about 1%" diameter. The crucible served as the cathode contact and a nickel wire anodic counter-electrode was suspended axially Within the crucible, but not touching the graphite 1 anthraquinone cake. A reference electrode (Ag, AgCl, N/ 10 aqueous HCl) rested on the cake.

Aqueous sodium hydroxide (1N) was continuously added to the crucible from a dropping funnel, the countier-electrode being kept covered with the electrolyte. The crucible and the counter-electrode were connected to a source of direct electric current. Suction was applied to the crucible to promote the flow of the electrolyte through the cake and a current of about 300 milliamperes was established at a potential not exceeding 1.01 volt. The filtrate was red in color. After about 1.5 hours, during which time about 200 milliliters of electrolyte had passed through the cake, the voltage rose to about 1.2 volt. The current was decreased to keep the voltage below 1.2 volts. The filtrate had a much lighter red color. Within about 15 minutes a current of only about 40 milliamperes could be passed without exceeding 1.2 volts. The cathode and counterelectrode were disconnected from the source of electrical current, and the cell system was flushed with additional electrolyte to make a total of about 400 milliliters.

The red filtrate containing anthrahydroquinone was treated with sufficient hydrogen peroxide to completely decolorize the solution. The precipitated anthraquinone was separated by filtration, washed with water and dried. The anthraquinone weighed 0.94 g,

indicating that at least 94% of the original anthraquinone had been electrolytically reduced to anthrahydroquinone.

EXAMPLE 6 The general procedure of Example 4 was followed using a mixture of 1.0 g. of benzanthrone and 1.0 g. of carbon. A nickel wire anodic counter-electrode was used instead of the graphite rod. An electrical current of M5 milliamperes was passed through the cell. The orange colored filtrate contained the leuco of benzanthrone, which on contact with air was reoxidized to benzanthrone, a yellow precipitate.

When the above process was applied to vat jade green, the soluble leuco form of the dye was obtained.

EXAMPLE 7 An intimate mixture of equal weights of indanthrone and carbon black was slurried with lN aqueous sodium hydroxide and the mixture was collected on a bed of diatomaceous filter aid placed on a sintered glass filter funnel. A graphite rod cathode contact was pressed against the cake and a nickel wire spiral anodic counter-electrode in a medium porosity fritted tube was suspended above the filter cake. The cathode and counter electrode compartments were filled with electrolyte I N aqueous sodium hydroxide solution). The contents of the filter funnel were heated by electrical tape.

Electrolysis was carried out with a direct current of about milliamperes at about l.O volt. The light brown filtrate contained the leuco of indanthrone which on contact with air became blue, indicating reoxidation to indanthrone.

EXAMPLE 8 A layer of 0.5 g. of graphite powder on a 56 stainless steel fritted filter disc mounted in a stainless steel pipe union was covered with 1.0 g. of anthraquinone without mixing the graphite and anthraquinone. The stainless steel filter disc and union served as the cathode contact and a nickel wire in a glass tube with fritted end served as the anodic counterelectrode. The electrolyte was 1N aqueous sodium hydroxide solution. During electrolysis an appreciable How of current occurred briefly and a red color appeared near the graphite. The current soon markedly decreased and remained low. Thereafter, the graphite and anthraquinone were throughly mixed, whereupon appreciable electrical current again was observed.

This example demonstrates the necessity for mixing the carbon and the material to be electrolyzed. The initial current flow was caused by slight mixing of graphite and anthraquinone at the interface of the two materials.

I claim:

6 l. A process for electrolyzing material capable of being oxidized or reduced comprising A. forming a liquid permeable mixture of a. conductor particles, said conductor particles 5 being of small particle size, electrically conductive, and insoluble in and unreactive to the electrolyte solution used in combination therewith, and b. material to be electrolyzed, said material being insoluble in and unreactive to the electrolyte solution used in combination therewith, in the physical form of particles of small particle size, and capable of being oxidized or reduced to yield products which are soluble in the electrolyte solution, in contact with an electrode and electrolyte solution, said electrolyte solution being capable of conducting electricity and of dissolving the products produced on oxidizing or reducing said material being electrolyzed but being incapable of dissolving said material to be electrolyzed or said conductor particles;

B. immersing a counter-electrode in said electrolyte solution out of contact with said liquid permeable mixture of particles; and

C. flowing electricity in a single direction between said electrode and said counter-electrode to oxidize or reduce said electrolyzable material thereby fonning a solution in said electrolyte of the resultant oxidized or red uced material.

2. A process as defined in claim 1 wherein said electrolyte solution reacts with said oxidized or reduced material to dissolve it.

3. A process as defined in claim 1 wherein said electrolyte solution dissolves said oxidized or reduced material without chemical reaction.

4. A process as defined in claim I wherein said conductor particles comprise carbon particles.

5. A process as defined in claim 1 wherein said step of forming a liquid permeable mixture in contact with an electrode and electrolyte solution comprises A. forming a slurry in said electrolyte solution of said conductor particles and said material to be electrolyzed,

A". filtering said slurry in a filter provided with means to conduct electricity to the base of the resultant filter cake, and

A'. continuously adding fresh electrolyte solution to maintain a body of electrolyte solution in contact with said filter cake while continuously withdrawing through said filter cake electrolyte solution containing dissolved therein the resultant oxidized or reduced material. 55 a: 

1. A PROCESS FOR ELECTROLYZING MATERIIAL CAPABLE OF BEING OXIDIZED OR REDUCED COMPRISING A. FORMING A LIQUID PERMEABLE MIXTURE OF A. CONDUCTOR PARTICLES, SAID CONDUCTOR PARTICLES BEING OF SMALL PARTICLE SIZE, ELECTRICALLY CONDUCTIVE, AND INSOLUBLE IN AND UNREACTIVE TO THE ELECTROLYTE SOLUTION USED IN COMBINATION THEREWITH, AND B. MATERIAL TO BE ELECTROLYZED, SAID MATERIAL BEING INSOLUBLE IN SAID UNREACTIVE TO THE ELECTROLYTE SOLUTION USED IN COMBINATION THEREWITH, IN THE PHYSICAL FORM OF PARTICLES OF SMALL PARTICLE SIZE, AND CAPABLE OF BEING OXIDIZED OR REDUCED TO YIELD PRODUCTS WHICH ARE SOLUBLE IN THE ELECTROLYTE SOLUTION, IN CONTACT WITH AN ELECTRODE AND ELECTROLYTE SOLUTION, SAID ELECTROLYTE SOLUTION BEING CAPABLE OF CONDUCTING ELECTRICITY AND OF DISSOLVING THE PRODUCTS PRODUCED ON OXIDIZING OR REDUCING SAID MATERIAL BEING ELECTROLYZED BUT BEING INCAPABLE OF DISSOLVING SAID MATERIAL TO BE ELECTROLYZED OR SAID CONDUCTOR PARTICLES; B. IMMERSING A COUNTER-ELECTRODE IN SAID ELECTROLYTE SOLUTION OUT OF CONTACT WITH SAID LIQUID PERMEABLE MIXTURE OF PARTICLES; AND C. FLOWING ELECTRICITY IN A SINGLE DIRECTION BETWEEN SAID ELECTRODE AND SAID COUNTER-ELECTRODE TO OXIDIZE OR REDUCE SAID ELECTROLYZABLE MATERIAL THEREBY FORMING A SOLUTION IN SAID ELECTROLYTE OF THE RESULTANT OXIDIZED OR REDUCED MATERIAL.
 2. A process as defined in claim 1 wherein said electrolyte solution reacts with said oxidized or reduced material to dissolve it.
 3. A process as defined in claim 1 wherein said electrolyte solution dissolves said oxidized or reduced material without chemical reaction.
 4. A process as defined in claim 1 wherein said conductor particles comprise carbon particles.
 5. A process as defined in claim 1 wherein said step of forming a liquid permeable mixture in contact with an electrode and electrolyte solution comprises A''. forming a slurry in said electrolyte solution of said conductor particles and said material to be electrolyzed, A''''. filtering said slurry in a filter provided with means to conduct electricity to the base of the resultant filter cake, and A''''''. continuously adding fresh electrolyte solution to maintain a body of electrolyte solution in contact with said filter cake while continuously withdrawing through said filter cake electrolyte solution containing dissolved therein the resultant oxidized or reduced material. 